Fast-cure silylated polymer adhesive

ABSTRACT

The cure-through rate of one-part silylated polymer adhesive/sealant compositions is improved by the addition of a small but effective amount of an alcohol-free hydrophilic solvent. The composition is particularly suitable for packaging in aluminum or aluminum-lined cartridges.

FIELD OF THE INVENTION

The invention relates to one-part silylated polymer adhesive/sealantcompositions, and more particularly to the use of a hydrophilic solventto improve the cure-through rate of such adhesive/sealant compositions.

BACKGROUND OF THE INVENTION

Compositions containing vulcanizable silicon terminated organic polymersare well known in the art, and are commonly used as adhesives and/orsealants. For example, U.S. Pat. No. 3,632,557, incorporated herein byreference, describes room temperature curable silicon terminated organicpolymers made by the reaction of an isocyanate terminated polyurethaneprepolymer having urethane linkages and an organic silicon compound.Such polymers are commonly referred to as silylated polymers, and finduse as adhesives and sealants, particularly in the automobile industry.Other patents relating to silylated polymers include U.S. Pat. Nos.3,979,344; 4,222,925; 4,889,903; 4,894,426; 4,954,598 and 5,097,053, allincorporated herein by reference.

It is often desirable to provide such silylated polymer adhesive/sealantcompositions in packages suitable for direct application of the product.A popular, efficient and economical type of package is an aluminum oraluminum-lined cartridge. Unfortunately, it has been discovered thatsuch adhesive/sealant compositions often react with the aluminum, andcorrode through the sides of such cartridges. Once the compositioncorrodes through the cartridge and is exposed to moisture in air, thecuring process begins, and the adhesive/sealant solidifies before it canbe used.

In using such adhesives and/or sealants, there are two important curerates which need to be considered. The first is the surface cure rate,generally expressed as the tack-free time, that is, the time until thesurface cures to the point of not being tacky. Generally, theapplication of the composition must be completed before such surfacecuring is complete. Therefore, the shorter the tack-free time, the lesstime one has to work with the adhesive/sealant. The second importantcure rate is the cure-through rate. This is a measure of the time whichit takes for the composition to cure through its thickness. The shorterthe cure-through time, the sooner the finished product can be used.Therefore, it is often desirable to speed up the cure through rate of anadhesive/sealant while maintaining or even increasing the tack freetime.

The present inventors made the discovery that methanol, which iscommonly used in formulations of such adhesive/sealant compositions,reacts with aluminum when in the presence of the catalysts whichnormally are also included in such compositions. In an attempt toovercome the corrosion problem, the present inventors testedcompositions prepared without methanol. Such compositions were found tobe non-reactive with aluminum, and therefore to have a much longer shelflife in aluminum cartridges. Unfortunately, it was also found that thecure-through rate of silylated polymer adhesives and/or sealants withoutmethanol was significantly slower than that of such adhesives/sealantswith methanol. Increasing the amount of catalysts and using differentcatalyst systems did not improve the cure-through rate. In some cases,adding additional catalyst or using alternate catalysts was found todecrease the tack-free time significantly, thus making theadhesive/sealant more difficult to handle, but without improving thecure-through rate. Thus, there is a need for a methanol-free silylatedpolymer adhesive/sealant composition which is non-corrosive to aluminumwith at least as fast a cure-through rate as compositions containingmethanol.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, it was discovered that theaddition of a small amount of one or more hydrophilic solvents to aone-part silylated polymer based adhesive/sealant composition speeds upthe cure-through rate of such compositions. It was further discoveredthat the elimination of methanol solves the corrosion problem when suchcompositions are packaged in aluminum containers. Therefore, the presentinvention provides a silylated polymer-based adhesive/sealantcomposition comprising a small but effective amount of one or morehydrophilic solvents, which composition is substantially free ofmethanol and other alcohols. Adhesives and/or sealants made inaccordance with the present invention are non-reactive with aluminum andhave a faster cure-through rate than such compositions without thesolvent. For purposes of this application, an effective amount of such asolvent is that amount which speeds up the cure-though rate of anadhesive/sealant composition as compared to the same adhesive/sealantcomposition without the solvent. A suitable method for determining thecure-through rate is set forth below.

In addition to avoiding methanol, it is believed that alcohols otherthan methanol, such as ethanol or propanol, should also be avoided insuch compositions. Such alcohols may undesirably react with othercomponents, particularly the silane components, thus adversely affectingthe properties or performance of the adhesive/sealant compositions. Suchreactions may also result in the formation of methanol as a byproduct.Therefore, the compositions of the present invention desirably are freeof methanol and any other alcohols as well.

Another embodiment of the invention is a method of accelerating thecure-through rate of a one-part, moisture-curable silylatedpolymer-based adhesive/sealant composition comprising adding aneffective amount of an alcohol-free hydrophilic solvent to thecomposition.

A further embodiment of the present invention is a packagedadhesive/sealant composition comprising:

a) an aluminum or aluminum-lined package; and

b) a one-part, moisture-curable silylated polymer-based adhesive/sealantcomposition comprising a moisture-curable silylated polymer and aneffective amount of a hydrophilic solvent,

wherein the composition is sealed within the package, is substantiallyfree of alcohols and is non-reactive with the aluminum of the package.

Although applicants do not wish to be bound by a particular theory ofhow the invention works, it is believed that when the hydrophilicsolvent evaporates from the adhesive/sealant composition it createschannels for moisture to get into the adhesive/sealant and thereby curethe silylated polymer. If there is no hydrophilic solvent in thecomposition, then the moisture has more difficulty reaching the interiorof the uncured material. As a result, although the tack-free timeremains the same or even increases, the cure-through time issignificantly diminished.

Hydrophilic solvents are those which have an affinity with water.However, because the silylated polymer compositions are cured byexposure to water, the solvents should be as anhydrous as is reasonablypossible. Suitable hydrophilic solvents for use in the present inventionshould be highly volatile, and include those oxygen and/or nitrogencontaining organic solvents whose flash points are less than about 45°C. (open cup) and whose evaporation rates are at least 1, with n-butylacetate defined as having an evaporation rate of 1. However, alcoholsshould not be used in the solvent because of possible undesirablereactions with aluminum in the packaging or with other components of thecomposition. Suitable hydrophilic solvents include substituted orunsubstituted esters, ketones and amines, provided they are sufficientlyvolatile and non-reactive with the other components of the compositions.Among the hydrophilic solvents suitable for use in the present inventionare esters such as amyl formate, ethyl acetate, isopropyl acetate,n-propyl acetate, ethyl propionate, isobutyl acetate and n-butylacetate; ketones such as acetone, methyl ethyl ketone, methyl propylketone and methyl isobutyl ketone; amines such as isopropylamine,secbutylamine, n-amylamine, sec-hexylamine, ethylamine, ethylenediamine, propyl imine, acetonitrile, n-butyronitrile and morpholine;mixture of such solvents and mixtures of them with other anhydroussolvents, especially their azeotropes.

The small amount of hydrophilic solvent used in the composition is notcritical, but preferably should be as small as possible. Preferably nomore than about 10 percent by weight (wt %) is used, more preferablyless than about 6 wt %, and most preferably less than about 3 wt %. Toobtain the desired cure-through rate acceleration, preferably a minimumof about 0.1 wt % is used, more preferably at least about 0.5 wt %, andmost preferably at least about 1 wt %. Thus, the amount of hydrophilicsolvent used is desirably in the range of about 0.1 to about 10 wt %,preferably from about 0.5 to about 6 wt %, more preferably from about 1to about 3 wt %. All percentages herein are by weight unless indicatedotherwise.

The following test methods were employed in the examples set forthbelow. Tack-free time was measured in accordance with ASTM C679-87(Reapproved 1992) entitled "Standard Test Method for Tack-Free Time ofElastomeric Sealants," incorporated herein by reference. As indicated inthe ASTM standard, the test consists of lightly touching a surface of acuring sealant with a polyethylene film at regular intervals until thesealant does not attach itself to the film and the film appears cleanwhen peeled from the surface.

The cure-through rate of adhesive samples is measured by the followingprocedure. A sample of the test adhesive is prepared and conditioned to23° C. for at least 6 hours. A polyethylene container is provided whichis as least 45 mm in diameter and 10 mm in height, and purged with drynitrogen. The container is filled with the test adhesive, and the topsurface leveled with a spatula. The sample is placed in a 23° C. 50%relative humidity (RH) chamber, in which it cures from the top surfacedown. After 24 hours, the central thickness of the cured disk-like topportion of the sample is measured.

The materials used in the following examples are all commerciallyavailable and/or may be prepared by methods well known in the art, asdiscussed, for example, in some of the references incorporated byreference above.

EXAMPLE 1 Preparation of a Silylated Polyurethane Polymer

A typical silylated polyurethane polymer was prepared for use in testingthe present invention. The formulation of the silylated polyurethanepolymer was as follows:

                  TABLE 1                                                         ______________________________________                                        Raw Material                Amount, g                                         ______________________________________                                        PPG-2200 (2000 MW polyether diol from ARCO)                                                               1179.58                                           TDI-80 (toluene diisocyanate)                                                                             123.14                                            Toluene                     96.41                                             METACURE ™ T-1 (dibutyltin diacetate from Air Products)                                                0.58                                              Acetic Acid                 0.29                                              SILQUEST ® A-1110 (γ-aminopropyltrimethoxysilane                                                43.03                                             from OSi Specialties)                                                         ______________________________________                                    

All of the raw materials except the A- 1110 were charged to a clean anddry reactor. The temperature was raised to 60° C. and maintained forabout 2 hours. The A-1110 was not added until the NCO percentage droppedto 0.708. The temperature was then cooled down to 37.8° C. The NCOpercentage was reduced to zero in about 15 minutes. This completed theformation of the silylated polyurethane polymer.

EXAMPLE 2 Preparation of a Silylated Polyether Polymer

A typical silylated polyether polymer was prepared for use in testingthe present invention. The formulation of the silylated polyetherpolymer was as follows:

                  TABLE 2                                                         ______________________________________                                        Raw Material                Amount, g                                         ______________________________________                                        ACCLAIM ™ 12200 (12000 MW polyether diol from                                                          1348.27                                           ARCO)                                                                         SILQUEST ® Y-5187 (γ-isocyanatopropyltrimethoxysilane                                           123.14                                            from OSi Specialties)                                                         METACURE ™ T-1 (dibutyltin diacetate from Air Products)                                                0.58                                              Acetic Acid                 0.29                                              ______________________________________                                    

All of the raw materials were charged to a clean and dry reactor. Thetemperature was raised to 60° C. and maintained for about 3 hours untilall hydroxyl groups were consumed. This completed the formation of thesilylated polyether polymer.

EXAMPLE 3 Silylated Polyurethane Adhesive/Sealant Compositions

This example tests the tack-free times and cure-through rates ofadhesive/sealant compositions made with the silylated polyurethanepolymer of Example 1 with and without a hydrophilic solvent, in thiscase n-propyl acetate, in accordance with the present invention. Thesesamples were all prepared without methanol or any other alcohol. Testsamples were made as follows:

                  TABLE 3                                                         ______________________________________                                                           Amount, g                                                  Ingredient         A      B       C    D                                      ______________________________________                                        Polymer of Example 1                                                                             633.6  633.6   633.6                                                                              633.6                                  REGAL ® 300R (carbon black from                                                              300.0  300.0   300.0                                                                              300.0                                  Cabot Corp.)                                                                  POLYCAT ® DBU (l,8-diaza-bicyclo                                                             1.22   2.44    1.22 1.22                                   (5, 4, 0) undecene-7 from Air Products)                                       MFTACURE ™ T-1  1.22   2.44    1.22 1.22                                   SILQUEST ® A-1120, N-beta-                                                                   4.00   4.00    4.00 0.00                                   (aminoethyl)-gamma-aminopropyltri-                                            methoxysilane from OSi                                                        SILQUEST ® Y-5187                                                                            0.00   0.00    0.00 4.00                                   Toluene            60.00  57.56   30.00                                                                              30.00                                  n-Propyl acetate   0.00   0.00    30.00                                                                              30.00                                  ______________________________________                                    

Tack-free times and cure-through rates were tested in accordance withthe abovedescribed procedures. The results were as follows:

                  TABLE 4                                                         ______________________________________                                                               A      B     C    D                                    ______________________________________                                        Tack-free time @ 23° C./50% RH, min.                                                          15     9     10   27                                   Cure-through rate @ 23° C./50% RH in 24 h, mm                                                 4.8    4.9   6.0  6.0                                  ______________________________________                                    

Sample A is a comparative example prepared without methanol or any otheralcohol, and also without any hydrophilic solvent. Sample B isessentially the same composition, but with twice the dosage of thecatalysts (POLYCAT® DBU and METACURE™ T-1). The results in Table 4 showthat the additional catalyst undesirably reduced the tack-free timewithout any significant effect on the cure-through rate. Sample C, whichincluded hydrophilic solvent in accordance with the present invention,had the same amount of catalyst as Sample A. Yet, the cure-through ratewas significantly improved over the rates of Samples A and B. Sample Dis another example using a hydrophilic solvent in accordance with thepresent invention. In this case, Y-5187 cyanato-silane was used insteadof A-1120 amino-silane. The cure-through rate was the same as that ofSample C, although the tack-free time was significantly increased. Thisshows that compositions can be made in accordance with the presentinvention which not only increase the cure-through rate, but alsoincrease the tack-free time. That is, while the total cure-through timeis shortened, the tack-free time, during which the adhesive/sealant isworkable, is increased. This data demonstrates that in comparison toother silanes, amino-silanes, such as SILQUEST® A-1120 or A-1110,shorten tack-free time without improving the total cure-through rate.

EXAMPLE 4 Silylated Polyether Adhesive/Sealant Compositions

Samples of silylated polyether adhesives were formulated as follows:

                  TABLE 5                                                         ______________________________________                                                              Amount, g                                               Ingredient            E      F                                                ______________________________________                                        Polymer of Example 2  673.6  673.6                                            REGAL ® 300R, carbon black                                                                      300.0  300.0                                            POLYCAT ® DBU, catalyst                                                                         1.22   1.22                                             MFTACURE ™ T-1     1.22   1.22                                             SILQUEST ® Y-5187, silane                                                                       4.00   4.00                                             Toluene               20.00  0.00                                             n-Propyl acetate      0.00   20.00                                            ______________________________________                                    

Tack-free times and cure through rates were tested as in the previousexample. The results were as follows:

                  TABLE 6                                                         ______________________________________                                                                  E     F                                             ______________________________________                                        Tack-free time @ 23° C./50% RH, min                                                              24    23                                            Cure-through rate @ 23° C./50% RH in 24 h, mm                                                    5.9   6.9                                           ______________________________________                                    

In this Example, Sample E was prepared with toluene, which is not ahydrophilic solvent, and Sample F was prepared with n-propyl acetate,which is a hydrophilic solvent in accordance with the present invention.The use of the hydrophilic solvent in Sample F significantly improvedthe cure-through rate without significantly affecting the tack-freetime.

EXAMPLE 5 MS Polymer Sealants

Sealant compositions were prepared from Kaneka MS Polymers, which aredescribed by the manufacturer as silyl-terminated polyethers fornon-isocyanate and moisture-curable polymer systems. Sample G wasprepared in accordance with the manufacturer's recommendations. Sample His identical to Sample G, except the amount of catalyst (NEOSTANN™ U220catalyst from Nitto Kasei Co) was doubled. Sample I is the same asSample G, except 45.9 g of a hydrophilic solvent (n-propyl acetate) wasadded in accordance with the present invention.

                  TABLE 7                                                         ______________________________________                                                                Amount, g                                             Ingredient              G      H      I                                       ______________________________________                                        S203H, MS polymer from Kaneka Corp.                                                                   300.0  300.0  300.0                                   S303H, MS polymer from Kaneka Corp.                                                                   200.0  200.0  200.0                                   DUP, plasticizer        275.0  260.0  229.0                                   Gama-Sperse ® CS-11, stearate surface modified                                                    600.0  600.0  600.0                                   calcium carbonate from Georgia Marble Corp.                                   TiO.sub.2               100.0  100.0  100.0                                   TINUVIN ® 327, 2-(5-chloro-2H-benzotriazole-                                                      10.0   10.0   10.0                                    2-yl)-4,6-bis (1,1-dimethylethyl)-phenol from                                 Ciba Geigy Co.                                                                TINUVIN ® 770, decanedioic acid, bis(2,2,6,6-                                                     10.0   10.0   10.0                                    tetramethyl-4-piperidinyl)ester from Ciba Geigy Co.                           SILQUEST ® A-171, vinyltrimethoxysilane                                                           10.0   10.0   10.0                                    from OSi                                                                      SILQUEST ® A-1120, N-beta-(aminoethyl)-                                                           15.0   15.0   15.0                                    gamma-aminopropyltrimethoxysilane from OSi                                    NEOSTANN ™ U220 catalyst from Nitto Kasei Co.                                                      10.0   20.0   10.0                                    n-Propyl acetate        0.0    0.0    45.9                                    ______________________________________                                    

Tack-free times and cure-through rates were tested as in the previousexample. The results were as follows:

                  TABLE 8                                                         ______________________________________                                                                G      H      I                                       ______________________________________                                        Tack free time @ 23° C./50% RH, min.                                                           24     19     23                                      Cure-through rate @ 23° C./50% RH in 24 h, mm                                                  3.8    3.8    4.2                                     ______________________________________                                    

These results show that doubling the amount of catalyst in Sample Hreduced the tack-free time, but had no effect on the cure-through rate.On the other hand, adding hydrophilic solvent in Sample I increased thecure-through rate about 10% without significantly reducing the tack-freetime.

Having thus described a few particular embodiments of the invention,various alterations, modifications, and improvements will readily occurto those skilled in the art. Such alterations, modifications andimprovements as are made obvious by this disclosure are intended to bepart of this description though not expressly stated herein, and areintended to be within the spirit and scope of the invention. Theforegoing description is by way of example only, and not limiting. Theinvention is limited only as defined in the following claims andequivalents thereto.

We claim:
 1. An adhesive/sealant composition comprising:a) amoisture-curable silylated polymer selected from the group consisting ofsilylated polyurethane, silylated polyethers, and combinations thereof;and b) from about 0.1 to about 10 weight percent of a hydrophilicsolvent, wherein said composition is substantially free of alcohols andnon-reactive with aluminum; and wherein said composition has anaccelerated cure-through rate.
 2. The composition of claim 1 whereinsaid silylated polymer is selected from the group consisting ofsilylated polyurethanes, silylated polyethers, and combinations thereof.3. The composition of claim 1 wherein said hydrophilic solvent isselected from the group consisting of oxygen and nitrogen containingorganic solvents and mixtures thereof.
 4. The composition of claim 3wherein said hydrophilic solvent has a flash point of less than about45° C. (open cup) and an evaporation rate of at least 1, with n-butylacetate defined as having an evaporation rate of
 1. 5. The compositionof claim 4 wherein said hydrophilic solvent comprises one or moresolvents selected from the group consisting of esters, ketones, amines,mixtures of such solvents and mixtures of such solvents with othersolvents.
 6. The composition of claim 5 wherein said hydrophilic solventcomprises one or more esters selected from the group consisting of amylformate, ethyl acetate, isopropyl acetate, n-propyl acetate, ethylpropionate, isobutyl acetate and n-butyl acetate.
 7. The composition ofclaim 6 wherein said hydrophilic solvent comprises n-propyl acetate. 8.The composition of claim 1 wherein said hydrophilic solvent is presentin an amount of about 0.5 to about 6 weight percent.
 9. The compositionof claim 1 wherein said hydrophilic solvent is present in an amount ofabout 1 to about 3 weight percent.
 10. A method of accelerating thecure-through rate of a one-part, moisture-curable adhesive/sealantcomposition comprising a silylated polymer selected from the groupconsisting of silylated polyurethanes, silylated polyethers, andcombinations thereof; said method comprising adding from about 0.1 toabout 10 weight percent of an alcohol-free hydrophilic solvent to saidcomposition.
 11. The method of claim 10 wherein said silylated polymeris selected from the group consisting of silylated polyurethanes,silylated polyethers, and combinations thereof.
 12. The method of claim10 wherein said hydrophilic solvent is selected from the groupconsisting of oxygen and nitrogen containing organic solvents andmixtures thereof, and has a flash point of less than about 45° C. (opencup) and an evaporation rate of at least 1, with n-butyl acetate definedas having an evaporation rate of
 1. 13. The method of claim 12 whereinsaid hydrophilic solvent comprises one or more solvents selected fromthe group consisting of esters, ketones, amines, mixtures of suchsolvents and mixtures of such solvents with other solvents.
 14. Themethod of claim 13 wherein said hydrophilic solvent comprises one ormore esters selected from the group consisting of amyl formate, ethylacetate, isopropyl acetate, n-propyl acetate, ethyl propionate, isobutylacetate and n-butyl acetate.
 15. The method of claim 14 wherein saidhydrophilic solvent comprises n-propyl acetate.
 16. The method of claim10 wherein said hydrophilic solvent is present in an amount of about 0.1to about 10 weight percent, based on the total weight of thecomposition.
 17. The method of claim 16 wherein said hydrophilic solventis present in an amount of about 0.5 to about 6 weight percent.
 18. Themethod of claim 17 wherein said hydrophilic solvent is present in anamount of about 1 to about 3 weight percent.